Excalibur brings high-energy lasers closer to the field

The idea of using a laser beam as a precision “death ray” has been around since lasers were invented in the 1960s. And while lasers have proved effective in many fields — from printing to eye surgery to communications — a couple factors have limited their practical use on military platforms.

For one thing, a high-energy beam capable of causing destruction has considerable size, weight and power requirements, what the military calls SWoP. For another, atmospheric turbulence can interfere with a beam over long distances, causing distortion and lessening the strength of the beam.

The Defense Advanced Research Projects Agency may have mitigated those problems with a successful test of a 21-element optical phased array (OPA) developed under its Excalibur program.

The low-power array consists of three clusters, each only 10 centimeters across and each packed with seven fiber laser amplifiers. In a recent test, it was able to precisely hit as target seven kilometers (about 4.35 miles) away, while accurately correcting for atmospheric turbulence at a level beyond what’s possible with conventional optics, DARPA said.

The demonstration took place at what DARPA said was several tens of meters above the ground, where the atmosphere can have its most negative effects on military applications. Excalibur used a high-speed optimization algorithm that corrected for atmospheric effects in sub-milliseconds, proving that the laser array could stay on target even in severe atmospheric conditions, DARPA said.

“The success of this real-world test provides evidence of how far OPA lasers could surpass legacy lasers with conventional optics,” DARPA program manager Joseph Mangano said in announcing the test. “It also bolsters arguments for this technology’s scalability and its suitability for high-power testing. DARPA is planning tests over the next three years to demonstrate capabilities at increasing power levels, ultimately up to 100 kilowatts—power levels otherwise difficult to achieve in such a small package.”

The Excalibur program has set a goal of developing a 100-kilowatt-class high-energy laser, or HEL, in a compact, light, low-power scalable configuration that would work with existing weapons platforms but be about 10 times lighter than current high-powered lasers.

The program also has branched out to other areas. In October 2013, the agency awarded contracts to Northrop Grumman and Lockheed Martin to develop missile-destroying lasers to be mounted on unmanned or manned aircraft. The contracts were awarded under DARPA’s Endurance program, a scion of Excalibur.